Witnesses

Bukhari :: Book 3 :: Volume 48 :: Hadith 830

Narrated Abu Bakra:

A man praised another man in front of the Prophet . The Prophet
said to him, "Woe to you, you have cut off your companion's neck,
you have cut off your companion's neck," repeating it several times
and then added, "Whoever amongst you has to praise his brother
should say, 'I think that he is so and so, and Allah knows exactly
the truth, and I do not confirm anybody's good conduct before
Allah, but I think him so and so,' if he really knows what he says
about him."